This invention relates to apparatus and methods for use in oil and/or gas wells or the like and more particularly to apparatus and methods for testing a hydrocarbon producing formation and/or completing one or more hydrocarbon producing formations.
One method for testing a formation in a cased well includes running an electric line casing gun perforator in mud of sufficient weight to control the well pressure, perforating the casing adjacent the zone to be tested, and then withdrawing the perforating gun. Test tools are then run into the well on a pipe string with well pressure being controlled with casing fluid of appropriate weight. A packer is set to close the annulus and a valve is opened in the pipe string to permit fluids from the formation to flow through the pipe string to the surface.
Another method for testing a formation includes running a tool string on drill pipe into the cased borehole with the tool string including full opening test tools with a full opening valve, and a packer disposed on the tool string for packing off the annulus. The casing adjacent the zone to be tested is packed off with the packer and the full opening valve is then opened providing fluid communication between the flow bore of the tubing string and the lower packed off portion of the casing. A small through-tubing perforating gun is lowered on an electric line through the test tools, and the casing adjacent the zone is perforated. The wireline perforating gun is then lubricated out of the well. Although additional through-tubing perforating guns can be lowered into the well to cover zones with long intervals, only the first perforation can be done with an underbalance so as to provide a negative pressure towards the tubing flow bore from the formation.
The latter method is particularly troublesome in high temperature wells where the mud contains solids such as barite. When the valve opens and pressure is removed from the mud below the valve, the water boils causing the barite to harden in the string below the valve. This can prevent through tubing perforating guns from passing through the tool string.
Another method is disclosed in the Halliburton U.S. Pat. No. 2,169,559. In Halliburton, a formation tester, sub, packer, perforated pipe, perforating gun, and bull plug are all suspended on the end of a drill pipe string. The formation tester includes a limited opening valve and mandrel for opening the valve. The valve includes a depending rod extending through a gland located in the sub. Adjacent the gland are a number of passageways to permit fluid flow from a point beneath the sub and into the formation tester. The sub also includes a switch contact connected to a battery with an electrical conductor which extends downwardly through the packer and is connected to the perforating gun. The bull plug below the perforating gun may include a pressure recording apparatus. In operation, the packer is set to seal the lower portion of the well from the portion above the packer and the drill pipe is rotated and lowered causing the mandrel to open the valve in the formation tester. This automatically starts the firing of the gun since as the valve stem moves downwardly to unseat, the depending rod makes electrical contact with the electrical conductor in the sub to detonate the perforating gun. Any fluid in the formation then flows through the perforations and through the perforated pipe above the perforating gun. This fluid must then pass through the limited openings of the passageways in the sub and of the valve and into the drill pipe. After a sufficient length of time the drill pipe is raised thus lifting the mandrel off the valve stem to allow the valve to close. When the valve closes, a sample of the fluid from the formation is entrapped in the drill pipe. The packer is then released and the entire assembly is removed from the well with the entrapped sample.
As is now well known in the art of completing oil and/or gas wells, a perforating gun is lowered into the cased borehole and the well is perforated by shooting perforations through the casing, cement and into the hydrocarbon formation to permit the hydrocarbons to flow into cased borehole and up to the surface. U.S. Pat. No. 3,706,344 to Vann discloses suspending a packer and perforating gun on a tubing string, setting the packer to isolate the production zone, releasing the trapped pressure below the packer by opening the tubing string to fluid flow, actuating the perforating gun through the tubing string, and immediately producing the well through the tubing string upon perforation. One means for actuating the perforating gun includes dropping a bar through the tubing string to impact the firing head of the perforating gun.
However, after a borehole has been drilled into the ground and the casing cemented into position, well fluids fill the cased borehole with drilling mud and debris. The mud and debris gravitate towards the lower end of the cased borehole and tend to densify and congeal into a heavy layer of material. Such drilling mud and debris also will settle and congeal in the tubing string and collect around the firing head of the perforating gun. Further, other debris inside the tubing string such as flakes, rust, sand, scale and other material dropped into well from the surface, tend to collect in the bottom of the string. Often such debris becomes dislodged and falls down through the tubing string as the string is handled and lowered into the well. Again, these heavy particles and other suspended matter will gravitate to the bottom of the string where such contaminates densify into a heavy layer of material around the firing head.
In a perforating gun having a bar actuated gun firing head for example, it is possible for such contaminates to densify and collect about the gun firing head mechanism and become so compacted and viscous that the gun firing head cannot be sufficiently impacted to detonate the perforating gun. If the bar is unable to sufficiently strike the firing mechanism, the gun will not be detonated. The problem of debris and contamination is compounded when the string is left downhole for a substantial length of time.
The present invention overcomes these deficiencies as hereinafter described.